Users and Portals

Hi Everybody,

I am putting together an on premise design for Dynamics CRM for a few hundred internal users and about 200,000 external users.  Nothing can be cloud hosted due to information security.  The external users are not part of the internal organization.  I am a bit confused with how the external users are typically handled in this sort of system.  

First, is there a supported Microsoft alternative to ADXStudio Portal available, or is the ADXStudio Community Edition still a decent option?

If the external user connects through a portal, how is the user database itself handled?  For example, does the portal broker the users and store the data in the SQL database, or should I stand up an AD Forest specifically for them?

Thanks!